In a fixed vane or rolling piston compressor, the vane is biased into contact with the roller or piston. The roller or piston is carried by an eccentric on the crankshaft and tracks along the cylinder in a line contact such that the piston and cylinder coact to define a crescent shaped space. The space rotates about the axis of the crankshaft and is divided into a suction chamber and a compression chamber by the vane coacting with the piston. In a vertical, high side compressor an oil pickup tube extends into the oil sump and is rotated with the crankshaft thereby causing oil to be distributed to the locations requiring lubricant. In the case of non CFC or HCFC operation, such as HFC for example, there may be inadequate lubrication. One reason for this is that the chlorine in refrigerants such as Freon.RTM. reacts with compatible lubricants to produce a protective film or coating. Also, HFC refrigerants have different operating characteristics which can impact the lubrication function. R-410A, for example, has a higher operating pressure than any common refrigerant. An area of sensitivity to inadequate lubrication is the line contact between the vane and piston and can cause excessive wear.
The synthetic oils, such as an ester oil of one or more monocarboxylic acids like polyol ester oils (POE), used with the new refrigerants release dissolved refrigerants much more rapidly than mineral oil and, as a result, the maintenance of adequate oil pressure under transient conditions is more difficult. A characteristic of the POE oils is that because they are more polar they do not "wet" the surfaces of the more polar metals such as aluminum or tin as well as mineral oil. As a result, more polar metals must be supplied continuously with a flow of oil from the pump i.e. with POE oils the pump must replenish the oil film with minimal interruption. Synthetic HFC-miscible lubricants such as those of the polycarbonate and polyvinyl ether (PVE) types can be used. Mineral oils (MO) and alkylbenzene (AB) lubricants offer better lubricity for rubbing surfaces subjected to high PV operation, but they have poor miscibility in HFC refrigerants. These oils form adsorbed films on the rubbing surfaces that improve their ability to protect the surface under boundary lubrication conditions, i.e. in the absence of full film hydrodynamic lubrication. In some applications where the immiscibility of MO and AB in the HFC refrigerant has no adverse effect on oil return to the compressor and oil management in the system and in the compressor, these lubricants could be used in HFC system, such as Room Air-Conditioners (RACs).
Accordingly, it is very desirable to qualify a suitable oil for HFC applications. The relatively low PV index, corresponding to the oil's rheological effects, is speculated as the major contributor to the deficiencies of POE oils. Thus, as the oil film breaks down, a catastrophic degradation in lubricating ability occurs and presents problems inherent with the use of present POE oils in refrigeration compressor environments. Inherent with most HFC lubricant applications is the need for the addition of antiwear additives to compensate for the poor lubricating qualities of this type lubricant. These additives can be harmful to air conditioning systems unless properly qualified. This is not generally known in the air conditioning industry.